The present invention relates to a method of providing a representation of an optical scene by the Welsh-Hadamard transform, and to an image sensor implementing the method. Recently, computer networks and multimedia technology have been developing rapidly. Data compression has thus become an important topic. In particular, numerous encoding methods have appeared in the field of image compressions. Of the methods used, encoding sytems using orthogonal transforms make it possible, for given image quality, to obtain compression ratios that are better than those obtained by methods of the linear prediction type. In addition, orthogonal transform encoding systems are much less sensitive to errors, e.g. transmission errors, than are prediction systems.
Although very many transforms have been studied, only a few are actually used at present: the Karhunen-Loeve transform which theoretically provides the best results, but which remains difficult to implement; the discrete cosine transform (DCT) which constitutes a good approximation to the Karhunen-Loeve transform and is specified in certain standards, and which is easier to implement; and the Walsh-Hadamard transform which is well suited to digital computation.
Like the Fourier transform, the Walsh-Hadamard transform consists in resolving the signal in question into a set of base vectors that are orthogonal. The Walsh-Hadamard transform can also be applied to multi-dimensional signals. Unlike the Fourier transform, it resolves the signal in question into a set of vectors that are not sinusoidal.